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Volcanowatch

October 12, 2000

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Cracks in road at Haleakala's summit-volcanic or benign?

Sweeping vistas into Haleakala Crater are seen in the final stretch of road at Haleakala National Park, from the summit visitor center to the top of Red Hill. Some observers, however, focus their attention on the pavement, which is prominently cracked perpendicular to travel direction. Where cracks are first noticed, the road crosses the volcano's southwest rift zone. Consequently, the cracks are oriented parallel to the rift, as if they have opened in response to volcanic forces.

Some tour guides claim that volcanic swelling has lifted the volcano's summit as much as five feet higher than the 10,023-foot elevation currently posted on the sign at the top of Red Hill. But nothing is farther from the truth than this notion of Haleakala inflating and cracking like a loaf of baking french bread.

Haleakala's summit is surprisingly stable, according to several lines of evidence. A Global Positioning System (GPS) receiver maintained by the University of Hawai`i's Institute of Geophysics indicates that any change is below the level of detection-far less than 5 mm (1/5 inch). In order to keep tabs on the volcano's activity, we at the Hawaiian Volcano Observatory conduct our own surveys every two to five years. Our GPS findings are similar: no detectable motion.

Supporting anecdotal information comes from staff in the summit observatories used for solar observations and satellite tracking. They have problems enough with daily temperature changes. If ground spreading perturbed these facilities periodically, the task of repositioning mirrors would become onerous.

Nonetheless, cracks have segmented the asphalt every 10 to 20 m (30-60 ft) along the Red Hill road. When measured in April 1999, the cracks ranged from a few millimeters to as wide as 10 cm (4 inches), big enough to put your foot in. They almost always are oriented directly across the road's centerline. Where the road curves, the cracks fan around the curve. Cracking parallel to the centerline is rare.

So why the cracking? It has to do with the cindery substrate found at Haleakala's summit. David Kruse, a National Park Service employee charged with federal road contracts throughout the western region, says that these cracks are typical in all the "lava" parks, such as Lava Beds National Monument (northern California) or Craters of the Moon (Idaho). "In each case the roads are built on cinders where the temperature range is extreme," says Kruse. At Haleakala, most of the park's road is built on lava flows, but the final stretch is entirely on cinder cones. At the summit, the road is subject to daily temperature fluctuations of more than 33 degrees C (60 degrees F).

The pavement, built during a project between 1978 and 1980, is about 20-22 years old. The cracks in it will soon disappear, because a contract has been awarded to grind up that segment of road and repave it. Work should begin in the spring of 2001, and only time will tell how soon thereafter cracks will reappear.

Haleakala is volcanically inactive at this time but will become restless sometime in the future. Shallow earthquakes will make new cracks that cleave the roads, lava flows, and building foundations at the summit, if the next eruption is centered along the upper southwest rift zone. For now, however, the cracks tell us only about the behavior of roads on cinder cones.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the past week. Lava is erupting from Pu`u `O`o and flowing southeast through a tube system down to the flats below Pulama pali and beyond to the coast near Kamokuna. A breakout from the tube system was observed near the 2000-ft elevation, and this was feeding a surface flow in the area. Lava in the tube system is entering the ocean along a broad, 600-meter (2,000-foot) front located 1.6 km (1 mi) west-southwest of Waha`ula. The new lava delta extends up to 150 meters (500 ft) beyond the old coastline. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The active lava flows are hot and have places with very thin crust. The steam clouds are highly acidic and laced with glass particles.

There were no earthquakes reported felt during the week ending on October 12.


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Updated: October 16, 2000